In today's world, it is almost impossible to live without smart phones or gadgets. People use them for calling/SMS, GPS (Global Positioning System), Multi-media etc, facilities. But to run this device, one must recharge the battery or power source of smart devices. We all are using electricity to get our phone charged by charger. But imagine the situation, the amount of power that complete world using for charging? This power is generated by burning coals, gas or oils which are non-renewable and will be depleted soon. They are also harmful to our mother earth's atmosphere. So, one of the alternative option is to use 'renewable' energy sources like 'solar energy', 'geo-thermal energy', 'wind energy' etc., but again they are costlier during installation and can not be available to everywhere one desire to use or install.
On the other hand, we do not required to build separate power plant for charging purpose. We only need few watts of electric power to be generated by any suitable mean which gives us economical as well as beneficial power option suitable to everyone. We can use our human energy to generate sufficient power by ourselves. We can generate two types of energy, active and passive energy. The active energy is the energy generated by use of hand crank device. Passive energy is inherent energy possessed by our body parts like brain or heart beats. Pace maker, audio-visual devices installed in our body can be run by heart beats or brains. These energy sources are with us so, these can be available to use every time.